Overview

What a cataract looks like

What a cataract looks like

A cataract occurs when the lens of your eye becomes cloudy. Eventually, a cataract can advance to the degree of the one shown in this person's right eye.

How a cataract affects your vision

How a cataract affects your vision

Normal vision (left) becomes blurred as a cataract forms (right).

A cataract is a clouding of the normally clear lens of your eye. For people who have cataracts, seeing through cloudy lenses is a bit like looking through a frosty or fogged-up window. Clouded vision caused by cataracts can make it more difficult to read, drive a car (especially at night) or see the expression on a friend's face.

Most cataracts develop slowly and don't disturb your eyesight early on. But with time, cataracts will eventually interfere with your vision.

At first, stronger lighting and eyeglasses can help you deal with cataracts. But if impaired vision interferes with your usual activities, you might need cataract surgery. Fortunately, cataract surgery is generally a safe, effective procedure.

Symptoms

Signs and symptoms of cataracts include:

Clouded, blurred or dim vision

Increasing difficulty with vision at night

Sensitivity to light and glare

Need for brighter light for reading and other activities

Seeing "halos" around lights

Frequent changes in eyeglass or contact lens prescription

Fading or yellowing of colors

Double vision in a single eye

At first, the cloudiness in your vision caused by a cataract may affect only a small part of the eye's lens and you may be unaware of any vision loss. As the cataract grows larger, it clouds more of your lens and distorts the light passing through the lens. This may lead to more noticeable symptoms.

When to see a doctor

Make an appointment for an eye exam if you notice any changes in your vision. If you develop sudden vision changes, such as double vision or flashes of light, sudden eye pain, or sudden headache, see your doctor right away.

Causes

Most cataracts develop when aging or injury changes the tissue that makes up your eye's lens.

Some inherited genetic disorders that cause other health problems can increase your risk of cataracts. Cataracts can also be caused by other eye conditions, past eye surgery or medical conditions such as diabetes. Long-term use of steroid medications, too, can cause cataracts to develop.

How a cataract forms

The lens, where cataracts form, is positioned behind the colored part of your eye (iris). The lens focuses light that passes into your eye, producing clear, sharp images on the retina — the light-sensitive membrane in the eye that functions like the film in a camera.

As you age, the lenses in your eyes become less flexible, less transparent and thicker. Age-related and other medical conditions cause tissues within the lens to break down and clump together, clouding small areas within the lens.

As the cataract continues to develop, the clouding becomes denser and involves a bigger part of the lens. A cataract scatters and blocks the light as it passes through the lens, preventing a sharply defined image from reaching your retina. As a result, your vision becomes blurred.

Cataracts generally develop in both eyes, but not evenly. The cataract in one eye may be more advanced than the other, causing a difference in vision between eyes.

Types of cataracts

Cataract types include:

Cataracts affecting the center of the lens (nuclear cataracts). A nuclear cataract may at first cause more nearsightedness or even a temporary improvement in your reading vision. But with time, the lens gradually turns more densely yellow and further clouds your vision.

As the cataract slowly progresses, the lens may even turn brown. Advanced yellowing or browning of the lens can lead to difficulty distinguishing between shades of color.

Cataracts that affect the edges of the lens (cortical cataracts). A cortical cataract begins as whitish, wedge-shaped opacities or streaks on the outer edge of the lens cortex. As it slowly progresses, the streaks extend to the center and interfere with light passing through the center of the lens.

Cataracts that affect the back of the lens (posterior subcapsular cataracts). A posterior subcapsular cataract starts as a small, opaque area that usually forms near the back of the lens, right in the path of light. A posterior subcapsular cataract often interferes with your reading vision, reduces your vision in bright light, and causes glare or halos around lights at night. These types of cataracts tend to progress faster than other types do.

Cataracts you're born with (congenital cataracts). Some people are born with cataracts or develop them during childhood. These cataracts may be genetic, or associated with an intrauterine infection or trauma.

These cataracts also may be due to certain conditions, such as myotonic dystrophy, galactosemia, neurofibromatosis type 2 or rubella. Congenital cataracts don't always affect vision, but if they do they're usually removed soon after detection.

Risk factors

Factors that increase your risk of cataracts include:

Increasing age

Diabetes

Excessive exposure to sunlight

Smoking

Obesity

High blood pressure

Previous eye injury or inflammation

Previous eye surgery

Prolonged use of corticosteroid medications

Drinking excessive amounts of alcohol

Prevention

No studies have proved how to prevent cataracts or slow the progression of cataracts. But doctors think several strategies may be helpful, including:

Have regular eye examinations. Eye examinations can help detect cataracts and other eye problems at their earliest stages. Ask your doctor how often you should have an eye examination.

Quit smoking. Ask your doctor for suggestions about how to stop smoking. Medications, counseling and other strategies are available to help you.

Manage other health problems. Follow your treatment plan if you have diabetes or other medical conditions that can increase your risk of cataracts.

Choose a healthy diet that includes plenty of fruits and vegetables. Adding a variety of colorful fruits and vegetables to your diet ensures that you're getting many vitamins and nutrients. Fruits and vegetables have many antioxidants, which help maintain the health of your eyes.

Studies haven't proved that antioxidants in pill form can prevent cataracts. But, a large population study recently showed that a healthy diet rich in vitamins and minerals was associated with a reduced risk of developing cataracts. Fruits and vegetables have many proven health benefits and are a safe way to increase the amount of minerals and vitamins in your diet.

Wear sunglasses. Ultraviolet light from the sun may contribute to the development of cataracts. Wear sunglasses that block ultraviolet B (UVB) rays when you're outdoors.

Reduce alcohol use. Excessive alcohol use can increase the risk of cataracts.

A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.org," "Mayo Clinic Healthy Living," and the triple-shield Mayo Clinic logo are trademarks of Mayo Foundation for Medical Education and Research.